1. Field of the Invention
This invention relates to the field of lubricating metal sheet product suitable for use as food and beverage can stock. The invention specifically relates to manufacturing pre-lubricated tab and end stock from 5000 Series aluminum alloys (Aluminum Association designations) such as 5042, 5082 and 5182 aluminum. An improved tab and end can stock lubricating composition and method are also described herein.
2. Technology Review
The aluminum industry supplies can manufacturers with millions of pounds of coiled sheet product each year. These manufacturers convert such sheet product into can bodies, ends and tabs for beer, beverages and certain foodstuffs. A substantial portion of aluminum sheet product is coated with a lubricant composition on one or both outer surfaces, typically by the can maker, prior to fabrication of the can bodies, ends and/or tabs. Lubricant coatings for any packages of food or beverages must meet all applicable U.S. Food and Drug Administration (FDA) requirements.
Lubricants, including liquids and solids, are used in metal working operations to reduce friction and wear between the surface of metal being worked and surfaces of the apparatus carrying out a given metal working operation. Lubricants reduce friction and wear by separating the contacting surfaces in relative motion with a thin fluid film of an appropriate composition.
In addition to their friction and wear reducing characteristics, lubricant compositions are expected to fulfill certain other requirements for industrial usage. They should be easy to apply and remove, where removal is warranted; afford some protection to the metal surface during handling and storage; present no health hazards to persons coming in contact with the composition; and be inert to the surfaces in contact therewith. Some lubricants produce severe stains on the metal surfaces they contact. It is highly desirable to avoid the staining of metal surfaces by using a lubricant of appropriate composition or blend having the properties demanded by the particular conditions under which the metal product will be worked.
It is known to apply lubricant compositions to aluminum sheet products through numerous methods. One representative means employs a spray coater or atomizer as set forth in Grassel U.S. Pat. No. 4,839,202, the disclosure of which is fully incorporated by reference. With the latter device, a lubricant composition consisting of only dioctyl sebacate (DOS), or bis(2-ethylhexyl)sebacate, is electrostatically deposited at a rate of about 1 mg/ft.sup.2 on both outer surfaces of beverage can stock. The purchaser of such metal, the can manufacturer, typically uncoils such stock to apply a second lubricant thereon before feeding his metals into the can tab or end conversion press.
Still other known lubricant application means include passing sheet product through any of various applicators which generate fine droplets of lubricant for deposit on said sheet product with electrostatic assistance, or between one or more rotating roll pairs having at least some portion of a roll surface in contact with, cowered by material of or immersed in a lubricant reservoir. The lubricant composition/blend of this invention can be applied by any of the foregoing means. On a less preferred basis, the invention may be added to one or more solvents prior to sheet metal application, said solvent(s) being suitable for flashing off and recovery for reuse.